Eu preciso de óleo para fritar o alho.

Because the verb precisar usually takes the preposition de when it means to need.

• Eu preciso de óleo. = I need oil.
• Ela precisa de ajuda. = She needs help.

This is just part of how the verb is normally used in Portuguese. English says need something, but Portuguese usually says precisar de alguma coisa.

You may sometimes hear precisar without de, especially in informal speech, but for learners, precisar de is the safest and most standard pattern.

Yes. In Brazilian Portuguese, subject pronouns are often omitted when the verb form already makes the subject clear.

So both are natural:

• Eu preciso de óleo para fritar o alho.
• Preciso de óleo para fritar o alho.

Including eu can add emphasis, clarity, or contrast, but it is not required here.

Here, para means for or in order to, and it is followed by the infinitive fritar.

So:

• para fritar o alho = to fry the garlic / in order to fry the garlic

This is a very common structure in Portuguese:

• Comprei pão para fazer sanduíches. = I bought bread to make sandwiches.
• Preciso de água para cozinhar. = I need water to cook.

Portuguese often uses definite articles more than English does.

So o alho literally looks like the garlic, but in natural English it is often just garlic.

This is very common with food and general nouns:

• Vou comprar o arroz. = I’m going to buy rice.
• Ela cortou a cebola. = She cut the onion.

In this sentence, o alho sounds very natural because it refers to the garlic involved in the cooking context.

In Portuguese, alho often works like garlic in English: it can refer to the ingredient in a general or mass-noun sense.

So fritar o alho can mean fry the garlic in a general cooking sense.

If you want to be more specific, you could say:

• um dente de alho = a clove of garlic
• dois dentes de alho = two cloves of garlic

For example:

• Eu preciso de óleo para fritar dois dentes de alho.

Óleo is pronounced roughly like OH-lee-oh, with the stress on the first syllable.

A rough guide:

• ó = stressed o
• le = sounds like lee
• o = final o, often closer to oo in Brazilian pronunciation

So it comes out approximately as OH-lee-oo or OH-lee-oh, depending on accent and speed.

The accent mark in ó shows where the stress goes.

The tricky part is lh.

In Brazilian Portuguese, lh sounds like the lli in million for many English speakers, though not exactly the same.

So alho is roughly:

• AHL-yoo or AH-lyo

The lh is a special Portuguese sound, and the final o in Brazilian Portuguese often sounds like oo.

This same lh appears in words like:

• filho = son
• mulher does not have this sound, so do not use it there
• trabalho = work

Yes, fritar works and means to fry.

But in cooking, if you mean lightly frying garlic in a little oil, especially at the start of a recipe, Brazilians often also use refogar.

Compare:

• fritar o alho = fry the garlic
• refogar o alho = sauté the garlic / cook the garlic lightly in oil

So your sentence is correct, but depending on the exact cooking action, refogar may sound even more specific.

Here, preciso is the first-person singular form of the verb precisar:

• eu preciso = I need

It is not the adjective preciso meaning precise or exact.

Portuguese has both:

• Eu preciso de óleo. = I need oil.
• O relógio é preciso. = The clock is accurate.

Same spelling, different grammar and meaning.

Yes, a little.

The original sentence is very natural:

• Eu preciso de óleo para fritar o alho.

You could also say:

• Para fritar o alho, eu preciso de óleo.

This version emphasizes to fry the garlic first, as the purpose.

Both are correct. The original order is the most neutral and common in everyday speech.

Yes, depending on what kind of fat you mean.

• óleo = oil
• azeite = olive oil
• manteiga = butter
• banha = lard

For example:

• Eu preciso de azeite para fritar o alho.

In everyday Brazilian cooking, óleo often refers to cooking oil in general, such as soybean oil.

Yes, it is natural and correct.

A Brazilian speaker would understand it immediately. Depending on the cooking context, they might also say:

• Preciso de óleo para fritar o alho.
• Preciso de óleo para refogar o alho.

So the sentence is perfectly good, and it sounds like normal everyday Portuguese.